This invention relates to an electrical test probe having a signal-transmitting wire that transmits to an outside circuit the electrical signals that are retrieved by bringing a protruded end of the needle-like element into contact with a specified material
A conventional electrical test probe that is used as a contact probe for performing an electrical check of a conductor pattern or an electronic element and the like of a printed circuit board, has a conductive needle-like element and a holder that supports the needle-like element so that the element protrudes in an axial-line direction, and is such that a protruded end of the needle-like element is elastically energized by a coil spring in an axial direction so as to project the protruded end from the front end of the holder so that the protruded end is elastically brought into contact with a material or object to be checked, i.e., a contacted material.
Recently, (1) a fine pitch has been realized for a substrate for mounting semiconductor chips or TAB as objects to be electrically checked by using such a conductive needle-like element, (2) the processing velocity has been fixed, and (3) the chips have been miniaturized and thinned. When an object is electrically checked, it is necessary that electrical test probes, which are installed so as to correspond to each electrode (leads of a land and TAB) as a contacted material arranged at a fine pitch, are brought into contact with the object in their respective order.
For the purpose of coping with the above-mentioned fine-pitched materials, the pitch between the electrical test probes are narrowed; for example, a pitch of from 0.15 mm to 0.2 mm has been required. Also, for transmitting electrical signals from the electrical test probes to an outside circuit, a lead wire must be installed as a signal-transmitting wire, but it is difficult for the lead wires to be arranged so as not to cause interference between the adjacent wires for each electrical test probe under the above-mentioned condition that the contacts are arranged at a pitch of 0.2 mm or less.
For example, a conventional lead-wire attaching structure in an electrical test probe is shown in FIG. 6. As shown in FIG. 6, a diameter-enlarged shell 21a of a conductive needle-like element 21 and a compressed coil spring 22 for elastically energizing a needle 21b in a protruding direction (the lower portion of FIG. 6) are coaxially accepted in a through hole 23a within an intermediate-layer member 23. The upper- and lower-layer members 24 and 25 are then laminated in such a way so as to sandwich the intermediate-layer member 23 between them. The lower-layer member 25 contains a hole 25a, which has a diameter that is large enough to accept the needle 21b of the needle-like element 21 and small enough to prevent extraction of the needle-like element 21, because the bottom of the shell 21a is brought into contact with the lower-layer member 25. In addition, the upper-layer member 24 contains a hole 24a that is small enough in diameter to accept the lead wire 27, which is connected to the needle-like element 21 via a pipe-shaped connector 26 in the through hole 23a, and that is large enough so as to prevent extraction of the coil spring 22.
As shown in FIG. 7, the needle-like elements 21 and 28 are respectively coupled to each end of the coil spring 22, and the shells 21a and 28a are elastically energized in a manner so as to protrude the needles 21b and 28b of the needle-like elements 21 and 28 in opposite directions. The needle 28b of the needle-like element 28, which protrudes in a direction opposite to that of the needle-like element 21 that is to be contacted with the contacted material, protrudes upward via the small-diameter hole 24a of the upper-layer member 24 in such a manner as to be inserted into and elastically contacted with the pipe-shaped connector 26 that is mounted in a wiring plate 29 which is laminated on the top face of the upper-layer member 24.
However, as shown in FIG. 8, when a lead wire 27 is composed of a coated wire, each of the above-mentioned connectors is formed in a pipe shape having a hole 26a into which a core wire 27a can be inserted. The pipe-shaped connector 26 is used for facilitating a connection to the lead wire 27. When the outside diameter of the pipe-shaped connector 26 is 0.11 mm or less, so as to correspond to the above-mentioned pitch of 0.15 mm or less, it must have a wall thickness of 0.04, and the inside diameter of the pipe hole is approximately 0.07 mm. Thus, the diameter of the core wire 27a that is to be inserted into the hole 26a is approximately 0.07 mm.
However, an easy-to-get conductive wire suitable for the lead wire 27 is not suitable for use as a wiring material for an electrical checking probe, because the resistance of the above-mentioned wire with a diameter of approximately 0.07 mm is 2xcexa8 or more at a length of 300 mm. If a special low-resistance wire material is used, the problem is that the parts are more expensive.
For the purpose of solving the above problems and realizing an electrical test probe that is capable of the desired fine pitch without narrowing the diameter of the lead wire extremely, the electrical test probe of the present invention has multiple conductive needle-like elements that are wound in a spiral manner and are parallel to each other, a holder for supporting the needle-like element so that the element protrudes in an axial-line direction, and signal-transmitting wires, one of which is provided to each of said plural needle-like elements, for transmitting to an outside circuit the electrical signals that are retrieved by bringing the protruded end of the needle-like element into contact with the contacted material. The signal-transmitting wire is composed of a single wire, and a flat part is formed at one portion of the end on the electric-signals-input side of each signal-transmitting wire, and said flat part is directly accepted in said holder. Also, the end of the holder is open at a size that allows the signal-transmitting wire to pass but that prevents the flat portion of the wire to be extracted from the holder.
With this invention, the signal-transmitting wire can be affixed to the holder end simply by only forming one end of the signal-transmitting wire, which is composed of a single wire, as a flat portion. As a result, a pipe-like connector does not need to be used. Also, because the signal-transmitting wire does not have to be thinner than is necessary for it to be inserted into the hole of the pipe-shaped connector, whose diameter is narrowed as necessary to achieve fine pitching, it is possible both to prevent the increase of conductive-wire resistance that results when the diameter of the signal-transmitting wire is made smaller, and to realize fine pitching.
In particular, it is preferable that the end of the holder is formed of a member that contains a stepped diameter axial-line through hole, with the larger-diameter portion being large enough to directly accept the flat portion of the signal-transmitting wire and the smaller-diameter portion being large enough to pass the wire but small enough to prevent extraction of the flat portion of the wire. As a result, because the flat portion is accepted by the bore-processed member and is prevented from being extracted, the holder end that prevents extraction can be easily processed and attached.
Or, it is preferable that the end of the holder is formed in a manner so as to laminate (1) a first laminar element that contains an axial-line through hole whose diameter is large enough to directly accept the flat portion of the signal-transmitting wire, and (2) a second laminar element that contains an axial-line through hole, whose diameter is large enough to pass the signal-transmitting wire but small enough to prevent extraction of the flat portion of the wire. Because the hole for accepting the flat portion and the hole for preventing extraction are in separate laminar elements, each bore-processing procedure can be easily applied.